Zainul Abideen

The place of halophytes in Pakistan’s biofuel industry

An unsustainable supply of fossil fuel necessitates the need to look for suitable alternatives. One solution lies in using plant biomass, which can be converted into a wide range of biofuels. To avoid conflict between feed and fuel, the crops available for human consumption being used presently as biofuel feedstock may be replaced with halophytes, which have the potential to thrive in saline lands and can be irrigated with brackish water; some can even tolerate seawater salinity. This approach will help in producing sustainable fuel without encroaching on the good quality land and water resources needed for food crops. A candidate species should preferably be perennial, having high yield in saline lands with minimum inputs. Other attributes include cellulose/hemicellulose >25–30%, lignin <10%, low salt load in foliage and a non-invasive nature. The unexplored aspects of agronomy of these wild plants need careful study, especially with regards to land degradation and ecological consequences, before large-scale cultivation.

Halophytic biofuels revisited

575 ISSN 1759-7269 10.4155/BFS.13.57

Importance of the Diversity within the Halophytes to Agriculture and Land Management in Arid and Semiarid Countries

Freshwater resources will become limited in near future and it is necessary to develop sustainable biological production systems, which can tolerate hyper-osmotic and hyper-ionic salinity. Plants growing in saline conditions primarily have to cope with osmotic stress followed by specific ion effects, their toxicities, ion disequilibrium and related ramifications such as oxidative burst. This is an exclusion criterion for the majority of our common crops. In order to survive under such conditions, suitable adjustments are necessary. Beside the control of the entrance on root level, the ability to secrete ions (excreter) or to dilute ions (succulents) helps to preserve a vital ion balance inside the tissues.

Oilseed halophytes: a potential source of biodiesel using saline degraded lands

The financial and technical aspects of using edible plants as a biodiesel source have been studied extensively, but research on the potential use of salt resistant, non-edible plants for this purpose remains relatively underexplored. Data available on salt tolerance range, seed oil content, composition of fatty acid methyl esters (FAME) and engine performance parameters – Iodine Value (IV), Cetane Number (CN) and Saponification Number (SN) – of 20 salt-resistant plants were examined to assess their suitability for use as diesel engine fuel. Most of the test species were perennial from family Amaranthaceae, exhibiting high salt tolerance. The quantity of their seed oil ranged from 10–30% while nine species contained >25% oil. The SN, IV and CN values varied from 130–206, 29–156 and 38–81, respectively. Based on the above mentioned parameters, seven halophytic plant species – Salicornia fruticosa, Cressa cretica, Arthrocnemum macrostachyum, Alhagi maurorum, Halogeton glomeratus, Kosteletzkya virginica and Atriplex rosea – appear to be promising biodiesel candidates. These non-food plants which can grow using saline resources and have an oil composition suitable for engine efficiency are more salt resistant than Jatropha or other glycophytic feedstock to serve in a bioenergy farming system. Cultivation of such plants for biodiesel production has the additional advantage of reclaiming degraded lands with the environmental benefit of carbon sequestration.

Growth patterns of Phragmites karka under saline conditions depend on the bulk elastic modulus

Salt stress is known to hamper steady-state water flow, which may reduce plant growth. This research was aimed to study the roles of leaf turgor, osmotic adjustment and cell wall elasticity under saline conditions which may reduce biomass production in Phragmites karka (Retz.) Trin, ex. Steud. (a marsh grass). Plants were grown in 0, 100 and 300 mM NaCl and harvested on 3, 7, 15 and 30 days to observe periodic changes in growth and water relations. Leaf number, relative growth rate, and relative elongation rates were higher in the non-saline control than in the plants grown under saline conditions. Plants showed a rapid decline in leaf growth rate (7–15 days) in 300 mM NaCl compared with a delayed response (15–30 days) in 100 mM NaCl. Leaf water potential decreased with increases in salinity after the third day of exposure whereas osmotic potential decreased after the fifteenth day. Low leaf turgor (Ψp) on the third day indicated an initial phase of osmotic stress under saline conditions. Plants maintained higher Ψp in 0 and 100 mM than in 300 mM NaCl. Differences between mid-day and pre-dawn water potential and water saturation deficit were higher in 300 mM NaCl than with other treatments. Water potential and hydraulic capacitance at turgor loss point decreased whereas bulk elastic modulus increased in 300 mM NaCl. Maintenance of turgor and growth at 100 mM NaCl could be related to efficient osmotic adjustment (use of K+ and Cl–), higher WUEi, and lower bulk elasticity whereas poor growth at 300 mM NaCl may have been a consequence of low turgor, decreased cell hydraulic capacitance and higher bulk elastic modulus.

Salinity improves growth, photosynthesis and bioenergy characteristics of Phragmites karka

Abstract. Based on biomass composition of plants collected from saline habitats, Phragmites karka (Retz.) Trin. ex Steud. has emerged as a suitable feedstock for biofuel. In the present study, plant growth, eco-physiological responses and bioenergy characteristics of P. karka grown under conditions ranging from non-saline to ∼80% seawater salinity are reported. Moderate salinity (NaCl at 100 mol m–3) increased plant fresh weight (20%), number of leaves (25%) and specific plant length, which were directly linked with increased net photosynthetic rate (25%) and stomatal conductance (25%) compared with the non-saline control. Higher photosynthetic efficiency was achieved by increasing electron transport rate (ETR, 20%), effective quantum yield (YII, 21%) and maximum efficiency of photosystem II (Fv/Fm, 20%). Decreased non-photochemical quenching (Y(NPQ)) and malondialdehyde content (18%) indicated an oxidative balance, which was also reflected in total carotenoids and chlorophylls. These eco-physiological parameters worked together to increase cellulose (34%) and hemicellulose (70%) at NaCl concentrations up to 200 mol m–3. Decreased growth under higher salinity could be linked with photosynthesis inhibition, due to stomatal closure and co-occurring reduction in CO2 uptake. Lower stomatal conductance increased water-use efficiency but led to over-production of reactive oxygen species, which disturbed oxidative stability (increasing ETR/PN) and imposed membrane leakage. Consequently, plants accumulated more carotenoids and soluble carbohydrates to stabilise PSII machinery (Fv/Fm, YII and Y(NPQ)), and to survive under high salinity. Such adaptations, however, led to growth penalty and reduced quality of lignocellulosic biomass. The above findings suggest that P. karka qualifies as a suitable raw material for biofuel under moderate salinity.